Phosphor and method for manufacturing the same, and light-emitting device and display device using phosphor

ABSTRACT

A phosphor includes (Sr 1−x , Ba x ) 3 SiO 5  with 1&gt;x≧0.1 as a base material and europium (Eu) as an activator. The emission center wavelength of the phosphor is controlled to be 600 nm or more on the basis of the composition ratio of Sr, Ba, and Eu.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Japanese Priority PatentApplication JP 2008-132705 filed in the Japan Patent Office on May 21,2008, the entire content of which is hereby incorporated by reference.

BACKGROUND

The present application relates to a phosphor, and particularly to aphosphor that includes (Sr_(1−x), Ba_(x))₃SiO₅ as a base material andeuropium (Eu) as an activator and emits orange fluorescence, a methodfor manufacturing the phosphor, and a light-emitting device and adisplay device using the phosphor.

In recent years, blue light-emitting diodes (LEDs) mainly composed ofgallium nitride that can efficiently emit light in a blue lightwavelength range have been developed and are widely used. A whitelight-emitting device (white LED) has been developed by combining such ablue LED with a yellow phosphor, which emits yellow fluorescence underexcitation with light in a blue-light wavelength range radiated from theblue LED. Since the white LED has a spectrum covering a wide wavelengthrange, its brightness in consideration of a visibility curve is high.Therefore, the white LED is used for an optical device such as a displaydevice attached to a cellular phone or a camcorder. It is also used as abacklight of liquid crystal displays as a substitute for an existingsmall lamp or fluorescent lamp or the like. For example, (Y, Gd)₃(Al,Ga)₅O₁₂:Ce is used as a yellow phosphor.

The white LED achieved by combining a blue LED with a yellow phosphorhas a problem in that color rendering in a red-color region is low dueto lack of red-light emission. Accordingly, a red phosphor that emitsred fluorescence and an orange phosphor that emits orange fluorescencewhen excited with light in a blue-light wavelength range are activelydeveloped. However, a red phosphor with an emission wavelength of 600 nmor more necessarily has a high proportion of covalent bonds in itscrystal structure. Thus, only a few crystals are available, and sulfidesand nitrides are the crystals most reported as a red phosphor.

There are some reports about an orange phosphor composed of a silicateof an alkaline-earth metal.

Japanese Unexamined Patent Application Publication No. 2005-68269(paragraphs 0010 to 0014) (Patent Document 1) titled “PHOSPHOR ANDTEMPERATURE SENSOR USING THE SAME” provides the following descriptions.

A base material constituting a phosphor according to the application ofPatent Document 1 is a silicate of an alkaline-earth metal and isrepresented by a general formula M_(x)(SiO_(n))_(y), where n is a wholenumber of 3 or more, preferably 3 or more and 5 or less. In other words,silicon trioxide (SiO₃), silicon tetroxide (SiO₄), and silicon pentoxide(SiO₅) are preferred as the silicate. This is presumably because theycan form a suitable crystal structure as a base material of a phosphor.

In the general formula, M represents one or more kinds of alkaline-earthmetal elements. Examples of the alkaline-earth metals include magnesium(Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Amongthese alkaline-earth metals, Sr and Ba are preferred because they canform a suitable crystal structure as a base material of a phosphor. Analkaline-earth metal M can be particularly represented by (Ba_(1−a),Sr_(a)), where a is a mixed crystal ratio (0≦a≦1). In the generalformula, x and y each represents a whole number of 1 or more and x isdetermined in accordance with n and y. In the case of y=1 in the generalformula, x≧1 is preferred. This means that, comparing an alkaline-earthmetal with a silicate both contained in a base material on a molarbasis, the number of moles of the alkaline-earth metal is larger than orequal to that of the silicate. This is presumably because such acomposition is necessary to form a suitable crystal structure as a basematerial of a phosphor.

Examples of the silicate of the alkaline-earth metal that satisfies theconditions described above include Ba₃SiO₅, Sr₃SiO₅, (Ba_(1−a),Sr_(a))₃SiO₅, Ba₂SiO₄, and α-BaSiO₃. Among these, Ba₃SiO₅, Sr₃SiO₅, and(Ba_(1−a), Sr_(a))₃SiO₅ have a tetragonal Cs₃CoCl₅-type crystalstructure.

The phosphor includes a silicate of the alkaline-earth metal as a basematerial and lanthanoid ions as an activator, and is represented by ageneral formula, La:M_(x)(SiO_(n))_(y), where La is a lanthanoid. Thelanthanoid is one of europium (Eu) and cerium (Ce), and is contained inthe phosphor by taking form of Eu²⁺ if it is Eu and Ce³⁺ if it is Ce,for example. Eu or Ce is added to a base material as an oxide by takingform of Eu₂O₃ if it is Eu and CeO₂ if it is Ce. In this case, 0.001 to0.2 atomic percent of the lanthanoid (La) relative to 1 atom of thealkaline-earth metal (M) is preferably added. In the case of less than0.001 atomic percent, emission intensity decreases and sufficientbrightness is not achieved. In the case of more than 0.2 atomic percent,quenching of light called concentration quenching is likely to occur.

Examples of the phosphor include Eu²⁺:Ba₃SiO₅, Ce³⁺:Ba₃SiO₅,Eu²⁺:Sr₃SiO₅, Ce³⁺:Sr₃SiO₅, Eu²⁺:(Ba_(1−a), Sr_(a))₃SiO₅,Ce³⁺:(Ba_(1−a), Sr_(a))₃SiO₅, Eu²⁺:Ba₂SiO₄, Ce³⁺:Ba₂SiO₄, Eu²⁺:BaSiO₃,and Ce³⁺:BaSiO₃.

In Japanese Unexamined Patent Application Publication No. 2006-36943(paragraphs 0012 to 0014 and 0019 to 0020) (Patent Document 2) andJapanese Unexamined Patent Application Publication No. 2007-227928(paragraphs 0017 and 0027 and FIG. 4) (Patent Document 3), a Sr₃SiO₅phosphor is described, and Patent Document 2 titled “ORANGE PHOSPHOR”provides the following descriptions.

An orange phosphor according to the application of Patent Document 2 hasa single phase crystal structure represented by the general formula(Sr_(1−x), EU_(x))₃SiO₅ (0<x≦0.10) and exhibits a high-intensity orangelight emission with a peak at around 580 nm.

At a firing temperature of 1300° C. or more or when firing is conductedat more than 1300° C., a phosphor having a single phase crystalstructure that matches with a powder X-ray diffraction pattern ofSr₃SiO₅ registered in Joint Committee on Powder Diffraction Standards(JCPDS) Card No. 26-984 is achieved. This phosphor exhibits ahigh-intensity orange light emission with a peak at around 580 nm.

The orange phosphor has a crystal structure of Sr₃SiO₅ and a structurein which part of Sr is replaced with Eu as an activator. The ratio inwhich Sr is replaced with Eu is more than 0% but not more than 10% ofthe atomic weight of Sr. This is because light emission does not occurif Sr is not replaced with Eu. Furthermore, if more than 10% of Sr isreplaced with Eu, the phosphor does not exhibit a high-intensity lightemission due to photoexcitation in an ultraviolet to visible rangecaused by concentration quenching, formation of a multiphase crystalstructure, or the like.

In Non-Patent Document 1 (J. K. Park et al, “Embodiment of the warmwhite-light-emitting diodes by using a Ba²⁻ codoped Sr₃SiO₅:Euphosphor”, Appl. Phys. Lett., 88, 043511-1 to -3 (2006) (FIG. 1 and line12 in right column of 043511-1 through line 15 in right column of043511-2)), fluorescence spectra of Sr₃SiO₅:Eu samples ((Sr_(2.93−x),Ba_(x))SiO₅:Eu_(0.07) (x=0.0, 0.05, 0.10, and 0.20) as a function ofBa²⁺ concentration are described. In the description, the entire spectrashift to longer wavelengths as the Ba²⁻ concentration increases, and thepeak wavelength shifts from 570 to 585 nm. In addition, the secondphase, BaSi₄O₉ is formed when the Ba²⁺ concentration exceeds 0.5 mol.

Non-Patent Document 2 (H. S. Jang, W. B. Im and D. Y. Jeon: “Luminescentproperties of (Sr_(1−x)M_(x))₃SiO₅:Eu²⁺ (M=Ca, Ba) phosphor for whiteemitting light source using blue/near UV LEDs” Proc. IDW/AD'05 (2005)pp. 539-pp. 542) (FIG. 3, FIG. 4, Abstract, Results and discussion,Conclusion)) provides the following descriptions. When the number ofEu²⁺ ions in a Sr₃SiO₅ host lattice increases, a shift of the emissionwavelength to longer wavelengths is actually observed. Inphotoluminescence (PL) spectra of (Sr_(1−x), Ba_(x))₃SiO₅:Eu²⁺ having aBa concentration of 0 mol %, 20 mol %, 40 mol %, 60 mol %, and 80 mol %,when Sr sites are replaced with 20 mol % of Ba²⁺, the emission bandshifts to longer wavelengths, that is, a red shift occurs. When the Baconcentration exceeds 20 mol %, the emission band shifts to shorterwavelengths.

SUMMARY

In a white LED achieved by combining a blue LED and a yellow phosphor,color rendering in a red-color region is low due to lack of red-lightemission. To improve the color rendering, the development of a phosphorthat emits orange to red fluorescence by absorbing light in a blue-lightwavelength range (400 to 480 nm) is desired. Sulfide phosphors andnitride phosphors are exemplified as a red phosphor having an emissionwavelength of 600 nm or more. However, H₂S gas is necessary tosynthesize sulfide phosphors. Firing at high temperature and pressure inan expensive high-temperature-and-pressure firing furnace andcomplicated synthetic processes are necessary to synthesize nitridephosphors, which increases manufacturing cost. Since nitrides that arevulnerable to water are used as a starting material to synthesizenitride phosphors, such materials are dry-blended in a glove box.Therefore, paying attention to every detail is necessary for thesynthesis.

In Non-Patent Document 1, a (Sr_(2.93−x), Ba_(x))SiO₅:Eu_(0.07) phosphor(x=0.0, 0.05, 0.10, and 0.20) is described. In the description, the peakwavelength shifts from 570 to 585 nm as the Ba²⁺ concentration inSr₃SiO₅:Eu increases, and the shift stops at 585 nm. In addition,BaSi₄O₉ is formed when the Ba²⁺ concentration exceeds 0.5 mol.

Suppose that, in (Sr_(2.93−x), Ba_(x))SiO₅:Eu_(0.07) described inNon-Patent Document 1, Ba sites are replaced with Eu. Then, the basematerial of the phosphor is represented by (Sr_(2.93−x),Ba_(x+0.07))SiO₅. In the case of (1) x=0.2, the base material of thephosphor is represented by (Sr_(2.73), Ba_(0.27))SiO₅. In the case of(2) x=0.5, the base material of the phosphor is represented by(Sr_(2.43), Ba_(0.57))SiO₅. If the base materials of (1) and (2) arerepresented by (Sr_(1−x), Ba_(x))₃SiO₅, x=0.27/3=0.09 is given in thebase material of (1) and x=0.57/3=0.19 is given in the base material of(2).

Non-Patent Document 1 describes a (Sr_(2.93−x), Ba_(x))₃SiO₅:Eu_(0.07)phosphor including 7 mol % Eu serving as an activator, but not phosphorshaving Eu concentrations other than 7 mol %. Non-Patent Document 1 doesnot teach phosphors with peak wavelengths (emission center wavelengths)exceeding 585 nm or phosphors including (Sr_(1−x), Ba_(x))₃SiO₅ withx≧0.1 as the base material represented by (Sr_(1−x), Ba_(x))₃SiO₅ and Euas the activator. Furthermore, a phosphor including (Sr_(1−x),Ba_(x))₃SiO₅ with x≧0.2 as a base material and Eu as an activator is notdescribed.

Non-Patent Document 2 discloses PL spectra of Sr₃SiO₅:Eu²⁺ under 405nm-excitation when the Eu concentration is changed to 0.5 mol %, 1.0 mol%, 1.5 mol %, 2.0 mol %, and 3.0 mol %, and that the emission wavelengthshifts to longer wavelengths as the Eu concentration increases.Non-Patent Document 2 also teaches that, in PL spectra of (Sr_(1−x),Ba_(x))₃SiO₅:Eu²⁺ having a Ba concentration of 0 mol %, 20 mol %, 40 mol%, 60 mol %, and 80 mol %, the emission band shifts to longerwavelengths when the Ba concentration is 20 mol %, and to shorterwavelengths when the Ba concentration exceeds 20 mol %.

However, Non-Patent Document 2 does not teach a phosphor having a peakwavelength (emission center wavelength) exceeding 600 nm and including(Sr_(1−x), Ba_(x))₃SiO₅ with x≧0.1 as a base material represented by(Sr_(1−x), Ba_(x))₃SiO₅ and more than 3 mol % of Eu or 6 mol % or moreof Eu as an activator.

Accordingly, it is desirable to provide a phosphor that includes(Sr_(1−x), Ba_(x))₃SiO₅ with 1>x≧0.1 as a base material and europium(Eu) as an activator and that emits orange fluorescence, a method formanufacturing the phosphor, and a light-emitting device and a displaydevice using the phosphor.

An embodiment provides a phosphor including (Sr_(1−x), Ba_(x))₃SiO₅ with1>x≧0.1 as a base material; and europium (Eu) as an activator. Theemission center wavelength of the phosphor is controlled to be 600 nm ormore on the basis of a composition ratio of Sr, Ba, and Eu.

An embodiment also provides a method for manufacturing a phosphorincluding (Sr_(1−x), Ba_(x))₃SiO₅ as a base material and europium (Eu)as an activator, including the steps of preparing a mixture of compoundsrespectively including Sr, Ba, Si, and Eu, such that a molar ratio ofSr, Ba, and Si is Sr:Ba:Si=3(1−x):3x:1 where 1>x≧0.1, and a ratio of thenumber of moles of Eu to a total number of moles of Sr, Ba, and Eu is0.02 or more and 0.08 or less; and firing the mixture at 1300° C. ormore and 1700° C. or less. In the method, an emission center wavelengthis controlled to be 600 nm or more on the basis of a composition ratioof Sr, Ba, and Eu.

An embodiment also provides a light-emitting device that uses thephosphor described above.

An embodiment also provides a display device having the light-emittingdevice that uses the phosphor described above, as a light source usedfor irradiating a display section.

The phosphor according to an embodiment includes (Sr_(1−x), Ba_(x))₃SiO₅as a base material with 1>x≧0.1 and europium (Eu) as an activator andits emission center wavelength is controlled to be 600 nm or more on thebasis of the composition ratio of Sr, Ba, and Eu. Thus, a phosphor thatemits orange fluorescence and can improve color rendering in a red-colorregion can be provided.

The method for manufacturing a phosphor according to an embodimentincludes the steps of preparing a mixture of compounds respectivelyincluding Sr, Ba, Si, and Eu, such that the molar ratio of Sr, Ba, andSi is Sr:Ba:Si=3(1−x):3x:1 where 1>x≧0.1, and the ratio of the number ofmoles of Eu to the total number of moles of Sr, Ba, and Eu is 0.02 ormore and 0.08 or less; and firing the mixture at 1300° C. or more and1700° C. or less. Thus, a method for manufacturing a phosphor thatincludes (Sr_(1−x), Ba_(x))₃SiO₅ as a base material and Eu as anactivator, has an emission center wavelength of 600 nm or morecontrolled on the basis of the composition ratio of Sr, Ba, and Eu,emits orange fluorescence, and can improve color rendering in ared-color region can be provided. In the case where the ratio is 0.02 ormore and 0.08 or less, the emission intensity of the phosphor is about1.8 to about 2 times higher than that of a phosphor whose ratio is 0.1.

Since the light-emitting device according to an embodiment uses thephosphor described above, a light-emitting device that can improve colorrendering can be provided.

Since the display device according to an embodiment includes thelight-emitting device that uses the phosphor described above, as a lightsource used for irradiating a display section, a display device whosecolor rendering is improved can be provided.

Additional features and advantages are described in, and will beapparent from, the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graph showing fluorescence spectra of (Sr_(1−x),Ba_(x))₃SiO₅:Eu phosphors in Example of an embodiment;

FIGS. 2A and 2B are graphs showing a relationship between thecomposition x and fluorescence properties of (Sr_(1−x), Ba_(x))₃SiO₅:Euphosphors in Example of an embodiment;

FIG. 3 is a table showing the amounts of raw materials blended insynthesis of a (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphor (x=0.5), with avariety of Eu concentrations in Example of an embodiment;

FIG. 4 is a graph showing emission intensity as a function of the Euconcentration of the (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphor (x=0.5) inExample of an embodiment;

FIG. 5 is a table showing the amounts of raw materials blended insynthesis of (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphors (x=0.25, 0.5, and0.75; Eu=8 mol %) in Example of an embodiment;

FIG. 6 is a graph showing a measured X-ray diffraction pattern(principal part) of a Ba₃SiO₅:Eu phosphor in Example of an embodiment;

FIG. 7 is a graph showing a measured X-ray diffraction pattern(principal part) of a (Sr_(0.25), Ba_(0.75))₃SiO₅:Eu phosphor in Exampleof an embodiment;

FIG. 8 is a graph showing a measured X-ray diffraction pattern(principal part) of a (Sr_(0.5), Ba_(0.5))₃SiO₅:Eu phosphor in Exampleof an embodiment;

FIG. 9 is a graph showing a measured X-ray diffraction pattern(principal part) of a (Sr_(0.75), Ba_(0.25))₃SiO₅:Eu phosphor in Exampleof an embodiment;

FIG. 10 is a graph showing a measured X-ray diffraction pattern(principal part) of a Sr₃SiO₅:Eu phosphor in Example of an embodiment;

FIG. 11 is a graph showing a relationship between the composition x ofthe (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphors and measured X-ray diffractionpatterns (principal part) in Example of an embodiment;

FIG. 12 is a graph showing a relationship between the composition x ofthe (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphors and lattice constants derivedfrom the measured X-ray diffraction patterns in Example of anembodiment; and

FIG. 13 is a sectional view of a white light-emitting device in anembodiment of an embodiment.

DETAILED DESCRIPTION

In the phosphor according to an embodiment, preferably x≧0.2. Whenx≧0.2, a phosphor that has an emission center wavelength of 600 nm ormore and can improve color rendering in a red-color region can beachieved. Particularly in the case of x≦0.5, a phosphor that has ahigher fluorescence intensity than a yellow yttrium-aluminum-garnet(YAG) phosphor ((Y_(1.5), Gd_(1.5))(Al₂, Ga₃)O₁₂:Ce) emitting yellowfluorescence and that has an emission center wavelength of 606 nm ormore and can improve color rendering in a red-color region can beachieved. In the case of 0.5≧x≧0.1, the fluorescence intensity of a(Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphor is about 1.07 to about 1.20 timeshigher than that of the yellow YAG phosphor.

Preferably 0.8≧x. When 0.8≧x, a phosphor that has an emission centerwavelength of 600 nm or more and can improve color rendering in ared-color region can be achieved. Particularly in the case of x≦0.5, thephosphor has a higher fluorescence intensity than the yellow YAGphosphor. In the case of 0.5≧x≧0.1, the fluorescence intensity of a(Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphor is about 1.07 to about 1.20 timeshigher than that of the yellow YAG phosphor.

Preferably 0.5≧x. When 0.5≧x, a phosphor that has a higher fluorescenceintensity than the yellow YAG phosphor and that has an emission centerwavelength of 600 nm or more and can improve color rendering in ared-color region can be achieved. In the case of 0.5≧x≧0.1, thefluorescence intensity of a (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphor is about1.07 to about 1.20 times higher than that of the yellow YAG phosphor.

The concentration of the activator is preferably 2 mol % or more and 8mol % or less. At such a concentration, the emission intensity of thephosphor is about 1.8 to about 2 times higher than that of a phosphorhaving an activator concentration of 10 mol %. Thus, a phosphor that hasa high fluorescence intensity and can improve color rendering in ared-color region can be achieved.

The concentration of the activator is preferably 6 mol % or more and 8mol % or less. At such a concentration, the emission intensity of thephosphor is about 1.9 to about 2 times higher than that of a phosphorhaving an activator concentration of 10 mol %. Thus, a phosphor that hasa higher fluorescence intensity and can improve color rendering in ared-color region can be achieved.

The phosphor preferably emits fluorescence when excited with blue light.Such a phosphor can be excited by a light-emitting element that emitsthe blue light. A white light-emitting device can be configured bymixing the blue light and orange fluorescence emitted from the phosphor.In addition, a display element that uses the light-emitting device as alight source used for irradiating a display section can be achieved.“The blue light” mentioned herein means “light in a blue-lightwavelength range”, which has a wavelength of 400 to 480 nm (the sameshall apply hereinafter).

The phosphor is preferably synthesized by firing a mixture of compoundsrespectively including Sr, Ba, Si, and Eu at 1300° C. or more and 1700°C. or less, the mixture being prepared such that a molar ratio of Sr,Ba, and Si is Sr:Ba:Si=3(1−x):3x:1 where 1>x≧0.1, and a ratio of thenumber of moles of Eu to a total number of moles of Sr, Ba, and Eu is0.02 or more and 0.08 or less. In the case where 1>x≧0.1 and the ratiois 0.02 or more and 0.08 or less, the emission intensity of the phosphoris about 1.8 to about 2 times higher than that in the case where theratio is 0.1. Thus, a phosphor that has a high fluorescence intensity,emits orange fluorescence whose emission center wavelength is 600 nm ormore, and can improve color rendering in a red-color region can beachieved.

In the method for manufacturing the phosphor according to an embodiment,preferably x≧0.2. When x≧0.2, a method for manufacturing a phosphor thathas an emission center wavelength of 600 nm or more and can improvecolor rendering in a red-color region can be provided. Particularly inthe case of x≦0.5, a method for manufacturing a phosphor that has ahigher fluorescence intensity than the yellow YAG phosphor and that hasan emission center wavelength of 606 nm or more and can improve colorrendering in a red-color region can be provided. In the case of0.5≧x≧0.1, the fluorescence intensity of a (Sr_(1−x), Ba_(x))₃SiO₅:Euphosphor is about 1.07 to about 1.20 times higher than that of theyellow YAG phosphor.

Preferably 0.8≧x. When 0.8≧x, a method for manufacturing a phosphor thathas an emission center wavelength of 600 nm or more and can improvecolor rendering in a red-color region can be provided. Particularly inthe case of x≦0.5, a method for manufacturing a phosphor having a higherfluorescence intensity than the yellow YAG phosphor can be provided. Inthe case of 0.5≧x≧0.1, the fluorescence intensity of a (Sr_(1−x),Ba_(x))₃SiO₅:Eu phosphor is about 1.07 to about 1.20 times higher thanthat of the yellow YAG phosphor.

Preferably 0.5≧x. When 0.5≧x, a method for manufacturing a phosphor thathas a higher fluorescence intensity than the yellow YAG phosphor andthat has an emission center wavelength of 600 nm or more and can improvecolor rendering in a red-color region can be provided. In the case of0.5≧x≧0.1, the fluorescence intensity of a (Sr_(1−x), Ba_(x))₃SiO₅:Euphosphor is about 1.07 to about 1.20 times higher than that of theyellow YAG phosphor.

The concentration of the activator is preferably 2 mol % or more and 8mol % or less. At such a concentration, the emission intensity of thephosphor is about 1.8 to about 2 times higher than that of a phosphorhaving an activator concentration of 10 mol %. Thus, a method formanufacturing a phosphor that has a high fluorescence intensity and canimprove color rendering in a red-color region can be provided.

The concentration of the activator is preferably 6 mol % or more and 8mol % or less. At such a concentration, the emission intensity of thephosphor is about 1.9 to about 2 times higher than that of a phosphorhaving an activator concentration of 10 mol %. Thus, a method formanufacturing a phosphor that has a higher fluorescence intensity andcan improve color rendering in a red-color region can be provided.

The phosphor preferably emits fluorescence when excited with blue light.In this case, a method for manufacturing a phosphor that can be excitedby a light-emitting element that emits the blue light can be provided.In the method, a white light-emitting device can be configured by mixingthe blue light and orange fluorescence emitted from the phosphor. Inaddition, a display element that uses the light-emitting device as alight source used for irradiating a display section and a phosphor thatcan improve color rendering in a red-color region can be achieved.

In a light-emitting device according to an embodiment, the phosphor ispreferably excited by a light-emitting element that emits blue light. Inthis case, the phosphor emits orange fluorescence when excited with bluelight emitted from the light-emitting element, and the orangefluorescence is mixed with the blue light to realize a light-emittingdevice that emits white light with improved color rendering.

In a display device according to an embodiment, the phosphor ispreferably excited by a light-emitting element that emits blue light. Inthis case, the phosphor emits orange fluorescence when excited with bluelight emitted from the light-emitting element, and the orangefluorescence is mixed with the blue light to realize a light-emittingdevice that emits white light with improved color rendering. Since thedisplay device includes such a light-emitting device, a display devicewith intense light in a red-color region can be achieved.

Regarding a silicon pentoxide phosphor including (Sr_(1−x), Ba_(x))₃SiO₅as a base material and Eu as an activator, its fluorescence spectrumcharacteristics resulting from excitation with blue light are consideredto significantly vary on the basis of the composition ratio of Sr, Ba,and Eu. In other words, the width of a fluorescence spectrum, anemission center wavelength, and a peak fluorescence intensity areconsidered to vary on the basis of not only the composition ratio of Srand Ba but also that of Eu.

In the present application, the variation in the fluorescence spectrumcharacteristics of the silicon pentoxide phosphor based on thecomposition ratio of Sr, Ba, and Eu was examined. Consequently, aphosphor with a fluorescence spectrum having a high peak fluorescenceintensity in an orange-light wavelength range, an emission centerwavelength of 600 nm or more, and a broad distribution ranging from ayellow-light wavelength range to a red-light wavelength range wasobtained. It was found that the color rendering in a red-color regioncould be improved by using this phosphor.

The phosphor according to an embodiment includes (Sr_(1−x), Ba_(x))₃SiO₅with 1>x≧0.1 as a base material and Eu as an activator. The phosphor hasan emission center wavelength of 600 nm or more controlled on the basisof the composition ratio of the Sr, Ba, and Eu, is excited by light in ablue-light wavelength range (blue light; 400 to 480 nm), emitshigh-intensity orange fluorescence having an emission center wavelengthof 600 nm or more, and can improve color rendering in a red-colorregion. More preferably x≧0.2. Preferably 0.8≧x, and more preferably0.5≧x.

The concentration of the activator is preferably 2 mol % or more and 8mol % or less, more preferably 6 mol % or more and 8 mol % or less. Inthe case of 0.5≧x≧0.1, the fluorescence intensity of the (Sr_(1−x),Ba_(x))₃SiO₅:Eu phosphor is about 1.07 to about 1.20 times higher thanthat of the yellow YAG phosphor (Y_(1.5), Gd_(1.5))(Al₂, Ga₃)O₁₂:Ce. Inthe case where the concentration of the activator is 2 mol % or more and8 mol % or less, the emission intensity of the phosphor is about 1.8 toabout 2 times higher than that of a phosphor having an activatorconcentration of 10 mol %. In the case where the activator concentrationis 6 mol % or more and 8 mol % or less, the emission intensity of thephosphor is about 1.9 to about 2 times higher than that of a phosphorhaving an activator concentration of 10 mol %.

In the phosphor according to an embodiment, compounds respectivelyincluding Sr, Ba, Si, and Eu are weighed such that the molar ratio (oratomic ratio) of metal elements Sr, Ba, and Si is Sr:Ba:Si=3(1−x):3x:1where 1>x≧0.1 and the ratio (=N_(Eu)/N_(T)) (molar ratio or atomicratio) of the number of moles of Eu, N_(Eu) (or atomicity) to the totalnumber of moles of Sr, Ba, and Eu, N_(T) (N_(T)=3) (or total atomicityin a chemical formula of the phosphor) is 0.02 or more and 0.08 or less,preferably 0.06 or more and 0.08 or less. The phosphor is thensynthesized from the compounds. N_(Sr), N_(Ba), and N_(Eu) denote thenumbers of moles of Sr, Ba, and Eu, respectively, andNT=N_(Sr)+N_(Ba)+N_(Eu)=3.

In the case where the ratio described above is 0.02 or more and 0.08 orless, the emission intensity of the phosphor is about 1.8 to about 2times higher than that of a phosphor whose ratio is 0.1. In the casewhere the ratio described above is 0.06 or more and 0.08 or less, theemission intensity of the phosphor is about 1.9 to about 2 times higherthan that of a phosphor whose ratio is 0.1.

That is to say, powders of compounds respectively including Sr, Ba, Si,and Eu are weighed such that the resulting phosphor includes (Sr_(1−x),Ba_(x))₃SiO₅ with 1>x≧0.1 as a base material and Eu as an activator,where the Eu concentration (molar percent or atomic percent) is 2% ormore and 8% or less (0.02≦(N_(Eu)/N_(T))≦0.08), preferably 6% or moreand 8% or less (0.06≦(N_(Eu)/N_(T))≦0.08). The powders are mixed andcrushed to prepare a mixture.

The mixture is fired at 1300° C. or more and 1700° C. or less tosynthesize a phosphor. To achieve a phosphor having a desiredcomposition, the mixture is preferably fired at 1600° C. in an inert gasatmosphere containing 4% or less of hydrogen on a volume basis.

The compounds respectively including Sr, Ba, Si, and Eu are mainlyoxides, carbonates, oxalates, etc., but not limited to these. Thecompounds may be other inorganic salts or organic compounds such asorganic salts.

In the method for manufacturing the phosphor according to an embodiment,the mixture is prepared such that the emission center wavelength iscontrolled to be 600 nm or more on the basis of the composition ratio ofSr, Ba, and Eu; the molar ratio (or atomic ratio) of metal elements Sr,Ba, and Si is Sr:Ba:Si=3(1−x):3x:1 where 1>x≧0.1; and the ratio(=N_(Eu)/N_(T)) (molar ratio or atomic ratio) of the number of moles ofEu, N_(Eu) (or atomicity) to the total number of moles of Sr, Ba, andEu, N_(T) (N_(T)=3) (or total atomicity in a chemical formula of thephosphor) is 0.02 or more and 0.08 or less, preferably 0.06 or more and0.08 or less. The mixture is then fired to synthesize the phosphor.

In other words, the method for manufacturing the phosphor includes a rawmaterial preparation step of weighing the compounds respectivelyincluding Sr, Ba, Si, and Eu such that the Eu concentration (molarpercent or atomic percent) is 2% or more and 8% or less, preferably 6%or more and 8% or less, and then preparing a mixture by mixing andcrushing the compounds; and a firing step of firing the mixture at 1300°C. or more and 1700° C. or less. In the method, the emission centerwavelength is controlled to be 600 nm or more on the basis of thecomposition ratio of Sr, Ba, and Eu.

In the firing step, the mixture is preferably fired at 1600° C. for fourhours in an inert gas atmosphere containing 4% or less of hydrogen on avolume basis. As a result, the phosphor that includes (Sr_(1−x),Ba_(x))₃SiO₅ as a base material and Eu as an activator, emitshigh-intensity orange fluorescence with an emission center wavelength of600 nm or more, and can improve color rendering in a red-color regioncan be manufactured.

The emission intensity of the phosphor manufactured by the methoddescribed above having a Eu concentration of 2% or more and 8% or lessis about 1.8 to about 2 times higher than that of a phosphor having a Euconcentration of 10%. The emission intensity of the phosphor having a Euconcentration of 6% or more and 8% or less is about 1.9 to about 2 timeshigher than that of a phosphor having a Eu concentration of 10%.

An embodiment will now be described in detail with reference to adrawing.

EMBODIMENT

A phosphor according to an embodiment is excited by light in ablue-light wavelength range from 400 to 480 nm, has an emission centerwavelength of 600 nm or more, and includes (Sr_(1−x), Ba_(x))₃SiO₅ with1>x≧0.1 as a base material and Eu as an activator. Preferably x≧0.2,more preferably 0.8≧x, more preferably 0.5≧x. In the case of 0.5≧x≧0.1,the fluorescence intensity of the (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphor isabout 1.07 to about 1.20 times higher than that of the yellow YAGphosphor (Y_(1.5), Gd_(1.5))(Al₂, Ga₃)O₁₂:Ce.

The phosphor according to an embodiment can be suitably used for alight-emitting device and a display device. In particular, the phosphorcan be suitably used for a display device such as a liquid crystaldevice that uses a light-emitting device such as a white LED.

In the description hereinafter, a phosphor including (Sr_(1−x),Ba_(x))₃SiO₅ (1>x≧0.1) as a base material and Eu as an activator isrepresented by (Sr_(1−x), Ba_(x))₃SiO₅:Eu, where x represents thecomposition of a base material. A Eu concentration is represented by theratio (=N_(Eu)/N_(T)) (molar percent or atomic percent) of the number ofmoles of Eu, N_(Eu) (or atomicity) to the total number of moles of Sr,Ba, and Eu, N_(T) (N_(T)=3) (or total atomicity in a chemical formula ofthe phosphor). Particularly when the composition of elements of aphosphor is clearly described, the phosphor is represented by (Sr_(a),Ba_(b))SiO₅:Eu_(c) (a>0, b>0, c>0, a+b+c=3).

FIG. 13 is a sectional view of a white light-emitting device(light-emitting device, white LED) that uses the phosphor in anembodiment.

In a white light-emitting device 10, as shown in FIG. 13, an InGaN blueLED 14 is mounted on the bottom of a reflector cup disposed in a casing11 and the blue LED 14 is connected to terminal electrodes 13 throughbonding wires 15. The reflector cup has a depressed portion with areflecting surface to improve the directivity of light emission byreflection. The terminal electrodes 13 are connected to an externalpower source (not shown).

The blue LED 14 is sealed, for example, in a molding portion 16containing a transparent epoxy resin and dispersed orange phosphoraccording to an embodiment. A lens for adjusting a divergence angle ofemission light may be disposed on the upper surfaces of the moldingportion 16 and the casing 11.

The orange phosphor emits orange fluorescence when excited with light ina blue-light wavelength range emitted from the blue LED 14. The orangefluorescence is mixed with the light in a blue-light wavelength rangeemitted from the blue LED 14, and the white light-emitting device 10produces white light. White light emitted from an existing whitelight-emitting device achieved by combining a blue LED with a YAGphosphor that emits yellow fluorescence includes less red-lightcomponents and exhibits low color rendering in a red-color region.

Since white light emitted from the white light-emitting device achievedby combining the blue LED and the orange phosphor according to anembodiment is produced by mixing light in a blue-light wavelength rangeemitted from the blue LED with the orange fluorescence emitted from theorange phosphor, red-light components can be increased and colorrendering can be improved. Such a white light-emitting device can besuitably used as a backlight of liquid crystal displays.

Furthermore, the orange phosphor according to an embodiment can be mixedwith the YAG phosphor that emits yellow fluorescence. In other words,the orange phosphor according to an embodiment and the YAG phosphor thatemits yellow fluorescence can be mixed and dispersed, for example, in aresin constituting the molding portion 16 shown in FIG. 13 such as atransparent epoxy resin. This can further increase red-light componentsand improve color rendering to achieve a white light-emitting devicewith low color temperature. By using such a white light-emitting deviceas a backlight of a liquid crystal display, a liquid crystal displaywith brighter light in a red-color region can be achieved.

EXAMPLE

FIG. 1 is a graph showing fluorescence spectra of (Sr_(1−x),Ba_(x))₃SiO₅:Eu phosphors (the composition x of a base material=0.0,0.25, 0.5, 0.75, and 1.0) in Example of an embodiment.

In FIG. 1, the abscissa indicates wavelengths (nm) and the ordinateindicates relative fluorescence intensities. In the graph, (a) is afluorescence spectrum of a Ba₃SiO₅:Eu phosphor with x=1.0, (b) is afluorescence spectrum of a (Sr_(0.25), Ba_(0.75))₃SiO₅:Eu phosphor withx=0.75, (c) is a fluorescence spectrum of a (Sr_(0.5), Ba_(0.5))₃SiO₅:Euphosphor with x=0.5, (d) is a fluorescence spectrum of a (Sr_(0.75),Ba_(0.25))₃SiO₅:Eu phosphor with x=0.25, (e) is a fluorescence spectrumof a Sr₃SiO₅:Eu phosphor with x=0.0, and (f) is a fluorescence spectrumof a yellow YAG phosphor.

The yellow YAG phosphor is commercially available (Y, Gd)₃(Al,Ga)₅O₁₂:Ce whose ratio of elements constituting its base material isY:Gd=1:1 and Al:Ga=2:3, that is, (Y_(1.5), Gd_(1.5))(Al₂, Ga₃)O₁₂:Ce. InFIG. 1, the Eu concentration of each of phosphors is 8 mol %, and amethod for synthesizing the phosphors (a) to (e) is described below(refer to the descriptions regarding FIGS. 3 and 5).

In FIG. 1, the excitation wavelength is 450 nm. As shown in a spacebelow FIG. 1, the peak wavelengths (emission center wavelengths) offluorescence spectra of the phosphors (a) to (f) are 595 nm, 602 nm, 610nm, 608 nm, 588 nm, and 565 nm, respectively. The fluorescence spectrawere measured with a measurement system Florog 3 available from JOBINYVON that uses Xe as an excitation light source.

Each of the emission center wavelengths λ of the fluorescence spectra of(b) (Sr_(0.25), Ba_(0.75))₃SiO₅:Eu, (c) (Sr_(0.5), Ba_(0.5))₃SiO₅:Eu,and (d) (Sr_(0.75), Ba_(0.25))₃SiO₅:Eu is 600 nm or more, which is in anorange-light wavelength range. The fluorescence spectra, which containthe wavelength components of a yellow-light wavelength range and ared-light wavelength range, are broad.

FIGS. 2A and 2B are graphs showing a relationship between thecomposition x of a base material and fluorescence properties of(Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphors in Example of an embodiment, whichare drawn by organizing the results shown in FIG. 1.

FIG. 2A shows the peak wavelength (emission center wavelength) offluorescence spectra as a function of the composition x of a basematerial. FIG. 2B shows the relative fluorescence intensity offluorescence spectra as a function of the composition x of a basematerial. The relative fluorescence intensity is given as a relativevalue such that the fluorescence intensities of different phosphors canbe compared with each other. Thus, the peak intensity of any phosphorcan be used as a reference.

As shown in FIG. 2A, the peak wavelengths λ (emission center wavelength)of fluorescence spectra of (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphors shiftfrom 588 nm to longer wavelengths as the composition x increases fromx=0.0. At about x=0.4, the amount of the shift reaches its peak and amaximum peak wavelength of about 610 nm is achieved. As x furtherincreases to x=1.0, the emission wavelength shifts from the maximum peakwavelength to shorter wavelengths. At x=1.0, λ is 595 nm.

In the case of 1>x≧0.1, each of the emission center wavelengths λ of thefluorescence spectra of (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphors is longerthan the emission center wavelengths λ of the fluorescence spectra ofBa₃SiO₅:Eu and Sr₃SiO₅:Eu phosphors, and λ is more than 595 nm and themaximum peak wavelength is 610 nm. In the case of 0.8≧x≧0.1, each of theemission center wavelengths λ of fluorescence spectra is 600 nm or moreand the maximum peak wavelength is 610 nm. In the case of 0.62≧x≧0.2,each of the emission center wavelengths λ of fluorescence spectra is 606nm or more and the maximum peak wavelength is 610 nm.

As shown in FIG. 2B, the relative fluorescence intensity of (Sr_(1−x),Ba_(x))₃SiO₅:Eu phosphors increases as the composition x increases fromx=0.0, and reaches its peak at x=0.25. As x further increases to x=1.0,the relative fluorescence intensity decreases, and finally, the relativefluorescence intensity of a Ba₃SiO₅:Eu phosphor becomes lower than thatof a Sr₃SiO₅:Eu phosphor. In the case of x=0.25, the fluorescenceintensity of a (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphor is about 1.20 timeshigher than that of a yellow YAG phosphor (Y_(1.5), Gd_(1.5))(Al₂,Ga₃)O₁₂:Ce.

In the case where the composition x of a base material is 0.5≧x>0.1, therelative fluorescence intensity of the fluorescence spectra of(Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphors is higher than that of Ba₃SiO₅:Euand Sr₃SiO₅:Eu phosphors, and also higher than that of the yellow YAGphosphor (shown with a broken line). That is to say, in the case of0.5≧x≧0.1, each of the emission center wavelengths λ of fluorescencespectra is 600 nm or more, and the relative fluorescence intensity offluorescence spectra is higher than that of any one of the Ba₃SiO₅:Euphosphor, the Sr₃SiO₅:Eu phosphor, and the yellow YAG phosphor.

In the case of 0.5≧x≧0.2, each of the emission center wavelengths λ offluorescence spectra is 606 nm or more, and the relative fluorescenceintensity of fluorescence spectra is higher than that of the yellow YAGphosphor. In the case of 0.5≧x≧0.1, the fluorescence intensity of the(Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphor is about 1.07 to about 1.20 timeshigher than that of the yellow YAG phosphor.

As described above, a phosphor having an emission center wavelength of600 nm or more, which is in an orange-light wavelength range, and afluorescence spectrum with a broad distribution ranging from ayellow-light wavelength range to a red-light wavelength range wasobtained by controlling the composition ratio of Sr and Ba. With thisphosphor, color rendering in a red-color region can be improved.

An activator concentration dependency (Eu concentration dependency) ofthe fluorescence intensity of a (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphor willnow be described.

FIG. 3 is a table showing the amounts of raw materials blended insynthesis of a (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphor (x=0.5), with avariety of activator concentrations (Eu concentrations) in Example.

A (Sr_(0.5), Ba_(0.5))₃SiO₅:Eu phosphor including (Sr_(1−x),Ba_(x))₃SiO₅ with x=0.5 as a base material was synthesized such that thestoichiometric ratio (composition ratio) (molar ratio or atomic ratio)of metal elements Sr, Ba, and Si is Sr:Ba:Si=1.5:1.5:1 and the Euconcentrations are 2, 4, 6, 8, and 10 mol %.

As shown in FIG. 3, strontium carbonate, barium carbonate, silicondioxide, and europium oxide were used as compounds respectivelyincluding Sr, Ba, Si, and Eu. The powders of these compounds wereweighed and blended to prepare a mixture. Strontium carbonate, bariumcarbonate, silicon dioxide, and europium oxide available from KojundoChemical Laboratory Co., Ltd. were used.

Each of the powders was weighed and blended to synthesize (Sr_(0.5),Ba_(0.5))_(2.94)SiO₅:Eu_(0.06), (Sr_(0.5),Ba_(0.5))_(2.88)SiO₅:Eu_(0.12), (Sr_(0.5),Ba_(0.5))_(2.82)SiO₅:Eu_(0.18), (Sr_(0.5),Ba_(0.5))_(2.76)SiO₅:Eu_(0.24), and (Sr_(0.5),Ba_(0.5))_(2.70)SiO₅:Eu_(0.30), assuming that the activator Eu wasequally substituted for Sr and Ba of (Sr_(0.5), Ba_(0.5))₃SiO₅ as a basematerial.

FIG. 4 is a graph showing relative emission intensity as a function ofthe Eu concentration of a (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphor (x=0.5) inExample of an embodiment.

In FIG. 4, the abscissa indicates Eu concentrations (mol %) and theordinate indicates relative emission intensities (peak fluorescencespectrum intensities) at an excitation wavelength of 450 nm. Therelative emission intensity of phosphors at the peak wavelengths(emission center wavelengths) of their fluorescence spectra was measuredwith the excitation light source and the fluorescence spectrometer usedfor measuring the fluorescence spectra shown in FIG. 1 described above.As shown in FIG. 4, the relative emission intensity slowly increases asthe Eu concentration is changed from 2 mol % to 8 mol %. At these Euconcentrations, the emission intensity is about 1.8 to about 2 timeshigher than that at a Eu concentration of 10 mol %. After the Euconcentration exceeds 8 mol %, the relative emission intensity rapidlydecreases.

Accordingly, since the peak fluorescence spectrum intensity depends onthe composition ratio of Eu as described above, the Eu concentration ispreferably 2 mol % or more and 8 mol % or less, more preferably 6 mol %or more and 8 mol % or less. In the case where the Eu concentration is 6mol % or more and 8 mol % or less, the emission intensity of thephosphor is about 1.9 to about 2 times higher than that of a phosphorhaving a Eu concentration of 10 mol %.

A method for synthesizing a (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphor will nowbe described. At a Eu concentration of 8 mol %, (Sr_(1−x),Ba_(x))₃SiO₅:Eu phosphors with x=0.0, 0.25, 0.5, 0.75, and 1.0 weresynthesized.

FIG. 5 is a table showing the amounts of raw materials blended insynthesis of (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphors (x=0.25, 0.5, and0.75; Eu=8 mol %) in Example of an embodiment.

The (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphors including (Sr_(1−x),Ba_(x))₃SiO₅ with x=0.25, 0.5, and 0.75 as a base material weresynthesized, such that the molar ratio (or atomic ratio) of metalelements Sr, Ba, and Si is Sr:Ba:Si=3(1−x):3x:1, and the Euconcentration is 8 mol %.

As shown in FIG. 5, strontium carbonate, barium carbonate, silicondioxide, and europium oxide were used as compounds respectivelyincluding Sr, Ba, Si, and Eu. The powders of these compounds wereweighed and blended to prepare a mixture. Strontium carbonate, bariumcarbonate, silicon dioxide, and europium oxide available from KojundoChemical Laboratory Co., Ltd. were used.

Each of the powders was weighed and blended to synthesizeBa_(2.76)SiO₅:Eu_(0.24), (Sr_(0.21), Ba_(0.71))₃SiO₅:Eu_(0.24),(Sr_(0.46), Ba_(0.46))₃SiO₅:Eu_(0.24), (Sr_(0.71),Ba_(0.21))₃SiO₅:Eu_(0.24), and Sr_(2.76)SiO₅:Eu_(0.24), assuming thatthe activator Eu was equally substituted for Sr and Ba of (Sr_(1−x),Ba_(x))₃SiO₅ as a base material. The amounts of raw materials blended insynthesis of Ba_(2.76)SiO₅:Eu_(0.24) and Sr_(2.76)SiO₅:Eu_(0.24) areomitted.

Phosphors including (Sr_(1−x), Ba_(x))₃SiO₅ as a base material and Eu asan activator were synthesized as follows. After 20 g of the mixtureprepared by weighing and blending compounds as shown in FIGS. 3 and 5was placed into a 500 mL plastic bottle, 200 ml of ethanol and 200 g of5φ zirconia balls were added to the mixture. Ball mill mixing was thenconducted at 50 rpm for 30 minutes. The ball-milled mixture wassubjected to suction filtration and dried at 80° C. for three hours.

The atmosphere surrounding the dried mixture was created by supplying ahoming gas (an inert gas (argon, nitrogen, etc.) containing 4% by volumeor less of hydrogen) at 1 L/min and by raising the temperature at 300°C./min. The mixture was fired at 1600° C. for four hours in the hominggas atmosphere. The resultant fired product was crushed and powder X-raydiffraction patterns shown in FIGS. 6 to 10 were measured using an X-raydiffractometer (RADIII) available from Rigaku Co., Ltd. with a Ni filterand CuKα rays (wavelength 0.1541 nm).

FIG. 6 is a graph showing a measured X-ray diffraction pattern(principal part) of a phosphor including Ba₃SiO₅:Eu with x=1.0 as a basematerial in Example of an embodiment.

FIG. 7 is a graph showing a measured X-ray diffraction pattern(principal part) of a phosphor including (Sr_(0.25), Ba_(0.75))₃SiO₅:Euwith x=0.75 as a base material and synthesized by blending the rawmaterials shown in FIG. 5, in Example of an embodiment.

FIG. 8 is a graph showing a measured X-ray diffraction pattern(principal part) of a phosphor including (Sr_(0.5), Ba_(0.5))₃SiO₅:Euwith x=0.5 as a base material and synthesized by blending the rawmaterials shown in FIG. 5, in Example of an embodiment.

FIG. 9 is a graph showing a measured X-ray diffraction pattern(principal part) of a phosphor including (Sr_(0.75), Ba_(0.25))₃SiO₅:Euwith x=0.25 as a base material and synthesized by blending the rawmaterials shown in FIG. 5, in Example of an embodiment.

FIG. 10 is a graph showing a measured X-ray diffraction pattern(principal part) of a phosphor including Sr₃SiO₅:Eu with x=0.0 as a basematerial in Example of an embodiment.

In FIGS. 6 to 10, the abscissa indicates diffraction angles 2θ (degree)and the ordinate indicates relative diffraction intensities. Latticeconstants a and c were determined as follows using the X-ray diffractionpatterns shown in FIGS. 6 to 10, assuming that the (Sr_(1−x),Ba_(x))₃SiO₅:Eu phosphors are tetragonal. The unit of diffraction angle2θ is degree.

In the Ba₃SiO₅:Eu phosphor, a=7.30₂ nm and c=11.2₄ nm were obtained fromFIG. 6 using diffraction peaks at diffraction angles 2θ=28.4₅((h,k,l)=(2,1,1)), 2θ=29.1₅ ((h,k,l)=(2,0,2)), 2θ=31.8₀((h,k,l)=(0,0,4)), and 2θ=34.7₀ ((h,k,l)=(2,2,0)).

In the (Sr_(0.25), Ba_(0.75))₃SiO₅:Eu phosphor, a=7.25 nm and c=11.1₃ nmwere obtained from FIG. 7 using diffraction peaks at diffraction angles2θ=28.6₅ ((h,k,l)=(2,1,1)), 2θ=29.4₀ ((h,k,l)=(2,0,2)), and 2θ=32.0₅((h,k,l)=(0,0,4)).

In the (Sr_(0.5), Ba_(0.5))₃SiO₅:Eu phosphor, a=7.0₈ nm and c=10.9₆ nmwere obtained from FIG. 8 using diffraction peaks at diffraction angles2θ=29.35 ((h,k,l)=(2,1,1)), 2θ=30.0₅ ((h,k,l)=(2,0,2)), and 2θ=32.6₀((h,k,l)=(0,0,4)).

In the (Sr_(0.75), Ba_(0.25))₃SiO₅:Eu phosphor, a=7.0₂ nm and c=10.9₄ nmwere obtained from FIG. 9 using diffraction peaks at diffraction angles2θ=29.6₀ ((h,k,l)=(2,1,1)), 2θ=30.2₅ ((h,k,l)=(2,0,2)), and 2θ=32.7₅((h,k,l)=(0,0,4)).

In the Sr₃SiO₅:Eu phosphor, a=6.95 nm and c=10.7₆ nm were obtained fromFIG. 10 using diffraction peaks at diffraction angles 2θ=29.9₀((h,k,l)=(2,1,1)), 2θ=30.6₀ ((h,k,l)=(2,0,2)), and 2θ=33.3₀((h,k,l)=(0,0,4)).

FIG. 11 is a graph showing a relationship between the composition x of(Sr₁ x, Ba_(x))₃SiO₅:Eu phosphors (x=0.0, 0.5, and 1.0) and measuredX-ray diffraction patterns (principal part) in Example of an embodiment.

In FIG. 11, measured X-ray diffraction patterns at a diffraction angle2θ of 27° to 34° shown in FIG. 6 (Ba₃SiO₅:Eu phosphor), FIG. 8((Sr_(0.5), Ba_(0.5))₃SiO₅:Eu phosphor), and FIG. 10 (Sr₃SiO₅:Euphosphor) are superimposed on each other. A circle, a triangle, and asquare in FIG. 11 represent diffraction peaks derived from theBa₃SiO₅:Eu phosphor, the (Sr_(0.5), Ba_(0.5))₃SiO₅:Eu phosphor, and theSr₃SiO₅:Eu phosphor, respectively.

Referring to FIG. 11, the diffraction peak of the (Sr_(0.5),Ba_(0.5))₃SiO₅:Eu phosphor is present between the diffraction peaks ofthe Sr₃SiO₅:Eu phosphor and the Ba₃SiO₅:Eu phosphor. Thus, Vegard's Lawholds in this case, and a phosphor having a desired composition ratio,that is, Sr:Ba=1:1 is considered to have been synthesized.

FIG. 12 is a graph showing a relationship between the composition x of(Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphors (x=0.0, 0.25, 0.5, 0.75, and 1.0)and lattice constants a and c derived from the measured X-raydiffraction patterns in Example of the an embodiment.

FIG. 12 shows the derived lattice constants a and c (nm) as a functionof the composition x of (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphors. As shownin FIG. 12, the lattice constants a and c are plotted near dashed linesin the drawing and vary linearly with the composition x. Thus, Vegard'sLaw holds in this case, and a (Sr_(1−x), Ba_(x))₃SiO₅:Eu phosphor havinga desired composition x is considered to have been synthesized.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope and without diminishing itsintended advantages. It is therefore intended that such changes andmodifications be covered by the appended claims.

The application is claimed as follows:
 1. A method for manufacturing aphosphor including (Sr_(1−x), Ba_(x))₃SiO₅ as a base material andeuropium (Eu) as an activator, comprising: preparing a mixture ofcompounds respectively including Sr, Ba, Si, and Eu such that a molarratio of Sr, Ba, and Si is Sr:Ba:Si=3(1−x):3x:1 where 0.5≧x≧0.25, and aratio of the number of moles of Eu to a total number of moles of Sr, Ba,and Eu is 0.06 or more and 0.08 or less; and firing the mixture at 1600°C. or more and 1700° C. or less in an inert gas atmosphere containing 4%or less of hydrogen on a volume basis, wherein a peak emissionwavelength of the phosphor is 600 nm or more based on a compositionratio of Sr, Ba, and Eu.
 2. The method for manufacturing the phosphoraccording to claim 1 that emits fluorescence when excited with bluelight.